In the prior art it has been difficult, especially in connection with x-ray cassettes, to ascertain whether or not the cassette contains film without opening of the cassette. As a result of this inability, mistakes have often been made and either an empty cassette was used during an x-ray exposure, or a cassette was used more than once. In each instance, the intended x-ray had to be retaken, which is not only very wasteful with respect to time, but also exposes the patient to unnecessary amounts of radiation.
The prior art has suggested the use of an indicator for identifying if the cassette contains an x-ray film. For example, U.S. Pat. No. 4,248,172 and German Patent 825,947 disclose a small moveable button which is slideable between a first position wherein the button is flush with the exterior surface of the cassette, and a second position wherein the button was recessed from the exterior surface. If film is present, the button is prevented from falling into the second position and thus indicating the presence of film.
Another common feature in x-ray cassettes is the patient identification window. Typically, this feature consists of an opening through the cassette which is covered by a light-tight slideable shutter. In use, the cassette is placed in the patient identification camera which establishes a light-tight seal against the cassette surrounding the window; opens the shutter; optically transfers patient identification information onto the x-ray film contained within the cassette; closes the shutter; and retracts the sealing means.
It is also common in places where radiography is practiced in large volumes, such as in large hospitals, to provide machines which automate the unloading and reloading of x-ray cassettes. Typically, these machines are comprised of a light-tight chamber into which the x-ray cassette is passed or placed. The chamber contains a first mechanism to open the cassette and a second mechanism generally featuring a plurality of suction cups to pick up the film and remove it from the cassette. Such mechanisms often fail when the film, which has been pressed into intimate contact with the intensifying screen, sticks to the upper screen when the cassette is open and thus is not in the proper position to be picked up by the suction cup mechanism.
Intensifying screens are often used in cassettes in order to increase exposure of the x-ray film. However, there is often some loss in sharpness of the image that is formed. This loss in sharpness is related to the separation distance between the light-sensitive layers of the film, and the light-emitting layers of the intensifying screen. To minimize this loss in sharpness, intensifying screens are often held in intimate contact with the film. In typical x-ray prior art cassettes, this intimate contact is normally accomplished by mounting the screens on resilient foam pads which are adhered to the cassette when closed.
Applicant has invented an improved film presence indicator which will indicate the presence of film in the cassette regardless of the cassette orientation and will, in addition, indicate whether a patient identification window of the cassette has been actuated. Further, when a cassette is open for removal of the film, the film presence indicator will push the film away from the upper screen assuring that the film is in the proper location for extraction by automatic cassette loaders.